The present invention relates to delay lines. It relates particularly to linear dispersive delay lines of the type used, for instance, in compressive receivers.
Linear dispersive delay lines are employed in compressive receivers to compress chirped signals in time so that simultaneously occurring signals of different frequencies are compressed into pulses that can be resolved in time in accordance with the signal that gave rise to them. The type of delay line that has typically been used in the past is the acoustic-wave delay line, which is a strip of a material, such as aluminum, that can serve as a propagation medium for acoustic waves and is dispersive throughout a range of frequencies. That is, the propagation velocity of the acoustic waves in this range of frequencies is a significantly varying function of frequency, so the delay introduced by a given length of the delay line is, too. The particular velocity-versus-frequency relationship depends on the cross-sectional dimensions perpendicular to the direction of propagation, and these can be varied throughout the length of the delay line so that the delay-versus-frequency relationships of the various sections of the delay line together yield a desired delay-versus-frequency relationship different from that of any individual section. For compressive receivers, the relationship is linear: the delay difference for a given frequency difference is constant throughtout the frequency range.
Conventional linear dispersive delay lines are limited in both frequency and bandwidth. Few are operable above 1.0 GHz, and bandwidths achievable by such delay lines are rarely greater than 0.5 GHz. Additionally, such delay lines cause considerable attenuation in the process of converting from electromagnetic energy to acoustic energy.
It is an object of the present invention to extend the frequency range of linear dispersive delay lines and other delay lines having customized dispersion relationships. It is a further object to provide an improved delay line.